As a standard practice in the hydrocarbon industry, oil and gas wells are drilled using various types of drilling mud with a drilling rig. The drilling mud is a fluid made from a recipe of chemicals that serve many purposes such as circulating out the rock cuttings while drilling, lubricating, and cooling the drilling bit to reduce friction while drilling, maintaining a hydrostatic column that will prevent inadvertent production of hydrocarbons during the drilling process, and forming of a filter cake layer that will prevent fluid losses into the formation. However, with all the benefits of drilling mud, it brings a major disadvantage which is formation damage. This damage occurs as the drilling mud contains solids in the recipe which plug the pores of the rock formation and, as a result, significantly reduces the oil or gas production potential. Therefore, it is a common practice to remove this damage using acid treatments after the well is drilled and before the well is put in production mode.
The acid treatment is usually pumped using high pressure pumps located at the surface to the oil or gas bearing formations downhole through a well completion which serves as a conduit for fluid production or injection. There are generally two types of matrix stimulation completions. The first are single port systems, where there is only one large port in any given stage for the acid to be pumped through, and through which hydrocarbons are produced. The second type of matrix stimulation systems, are multiple port systems where there are several smaller ports with the objective of providing a better distribution of the pumped acid across the reservoir. These multiple port systems, like the single port systems, are regarded as permanent well completions. Within the many different multiple port systems available in the market today, are multiple port systems operated using a cutter, launcher, and receiver. The cutters, launchers, and receivers are regarded as permanent parts of this system and serve the specific function of opening these multiple ports (initially run downhole in a closed position) to provide a flow path for the acid treatment directly to the reservoir and then permit producing the oil or gas through these ports.
These downhole, multiple port, oil or gas well stimulation systems operated by movable plugs/cutter devices may include more than one stage along the reservoir. Each stage includes isolation packers to isolate a given stage from the next stage. Between the isolation packers there are a number of downhole ports for the acid to reach the formation and for hydrocarbons to be produced from that particular port. Initially, these ports are run downhole in a closed position. The ports are selectively opened using either isolation balls by themselves or a combination of isolation balls and movable plugs/cutters. There are several multiple port stimulation systems currently available in the market today. Opening of the ports allows for the pumping of acid into the zone of interest and then producing the well through the ports after the stimulation is complete.
For the case of the multiple ports system which include the use of a movable cutter device, at one end of any multiple port stage there is a launcher and at the other end of the stage is a receiver. The purpose of the launcher is to launch a cutter from the launcher end to the receiver end in order to open the series of downhole ports by cutting the closed portions of the ports which extend into the tubular's inner diameter. The cutters are a permanent part of this system. Generally, the cutter is attached to the launcher with screws that are designed to shear under a certain pressure. Such cutters are available in the industry and can be a small piece of tubing or moveable plug with a tapered end, a ball seat inside of it, and seals around the cutter body to seal against the inner diameter of the tubing. After it is launched, the cutter moves from one end of the stage to the other end at a high velocity and cuts the closed portions of the ports that extend into the inner diameter of the tubing, thereby opening the ports in the process. In order to apply pressure to launch the cutter, an isolation ball is typically pumped in the tubing which lands on a ball seat inside the cutter. As pumping continues, the ball seals against the ball seat inside the cutter and pressure builds in the tubing. Once a certain pressure is reached, the screws shear, freeing the cutter to be launched at high velocities to the other end of the stage where it lands and seals against the receiver (opening the ports in the process). In theory, this action should open all ports within that particular stage. After the first stage is opened, a second, upper stage is targeted where another, larger isolation ball is used. The ball lands on the cutter of the upper stage that has a larger ball seat. As pumping continues, pressure in the tubing increases and the cutter is launched to the receiver of the upper stage, and therefore opens the ports of the upper stage. After the ports have been opened in any particular stage, the acid treatment is pumped into the well and exits the completion through the multiple ports and is therefore distributed along the reservoir. The port locations downhole are designed to be spaced out in a way that will distribute the acid along the entire length of any particular stage for maximum acid exposure to the formation. After the acid treatment in all the stages is completed, the well is then flowed back, the balls are collected, and the well flows through the downhole open ports.
Sometimes, due to a variety of reasons, not all of the downhole ports are opened. Currently, the only means for confirming that all downhole ports have been opened is through physical exploring of the well. For instance, means of confirming that all downhole ports are open include the use of production logging tools or temperature sensitive coiled tubing that detects changes in temperature along the open ports (while producing), and thereby confirms the ports are open. However, these methods are expensive, time consuming, and require well intervention which will disrupt the well production and may result in safety concerns. A less expensive, more efficient means of confirming the opening of all downhole ports is needed.